# data[].attributes.body
Magnify posts by clicking ctrl+ on your computer

Reduce posts by clicking ctrl- on your computer

Watch all posted videos in the Padlet to assist learning this section

Watch all my posted teaching videos on Classroom as overview of each topic

Download PhET's DC Kit virtual Lab to physically build circuits yourself given to you in harder problems to assist understanding of circuit rules.

# data[].attributes.headline
Weighting of ELECTRIC CIRCUITS - Paper 1

# data[].attributes.subject
Weighting of ELECTRIC CIRCUITS - Paper 1

# data[].attributes.attachment_link.title
What Is Electricity? - Atomic Structure and Electron Flow

# data[].attributes.body
Current = The rate of flow of charge between two points in a circuit.

# data[].attributes.attachment_link.title
Current Flow: Conventional Current vs Electron Flow - Classroom Video

# data[].attributes.body
Metals consist of positive ions surrounded by a “sea” of delocalised electrons.

The delocalised electrons are free to move through the crystal structure.

When connected to a power source, the electrons all drift in the same direction which creates an electric current (flow of charge at a certain rate).

# data[].attributes.body
Voltage = Electrical energy transferred per unit positive charge between two points in a circuit.

VOLTAGE = The "PUSH" behind the charge in the circuit.
EMF = The total energy supplied per unit positive charge by the cell.

# data[].attributes.body
An ammeter measures current in a circuit.

An ammeter has VERY LITTLE RESISTANCE.

An ammeter is always connected in SERIES with components in a circuit, as it must allow all the current to flow through it in order to measure current.

A Voltmeter measures potential difference between two points in a circuit.

A voltmeter has GREAT RESISTANCE.

A Voltemeter must therefore always be connected in parallel with a component in a circuit, in order to measure the difference in potential energy between two points right before and after a resistor.

# data[].attributes.body
Resistance = A material’s opposition to the flow of current through it.

The factors that affect resistance of a resistor:

Length

Thickness

Temperature

Type of material (resistivity)

State the relationship between resistance and each of these factors, and give a reason for each relationship.

# data[].attributes.attachment_link.title
GCSE Science Revision - Factors affecting Resistance

# data[].attributes.body
3. Potentiometer (another type of variable resistor)

# data[].attributes.body
2. Variable resistor (rheostat)

# data[].attributes.body
1. Fixed resistors

# data[].attributes.headline
HOW TO CALCULATE TOTAL RESISTANCE IN SERIES VS PARALLEL

# data[].attributes.subject
HOW TO CALCULATE TOTAL RESISTANCE IN SERIES VS PARALLEL

# data[].attributes.body
Current through a conductor is directly proportional to potential difference across a conductor, provided the temperature of the conductor stays constant.
Therefore:
R = V/I

# data[].attributes.attachment_link.title
GCSE Science Revision - Resistance and Ohms Law

# data[].attributes.attachment_link.title
Basic Electricity:  Ohm's Law Instructional Video

# data[].attributes.body
EXPERIMENT

# data[].attributes.body
Watch this video on worked examples

# data[].attributes.body
When resistors are added in series, the total resistance increases.

When resistors are added in parallel, the total resistance decreases.

When a load is connected to a battery, the voltmeter connected across the battery will be the reading for 𝑉 𝑒𝑥𝑡.

# data[].attributes.headline
R4 is shorted out the circuit. No current passes through R4.

# data[].attributes.subject
R4 is shorted out the circuit. No current passes through R4.

# data[].attributes.headline
ELECTRIC POTENTIAL COLOUR CODING TECHNIQUE

# data[].attributes.subject
ELECTRIC POTENTIAL COLOUR CODING TECHNIQUE

# data[].attributes.body
Watch this video:

# data[].attributes.headline
HOW TO ANALYSE A CIRCUIT USING THE COLOUR CODING TECHNIQUE

# data[].attributes.subject
HOW TO ANALYSE A CIRCUIT USING THE COLOUR CODING TECHNIQUE

# data[].attributes.body
Red = High electrical potential
Blue = Low electrical potential

# data[].attributes.body
“La Dame de Fer” all aglow.

# data[].attributes.headline
Electrical lighting facts about the Eiffel Tower

# data[].attributes.subject
Electrical lighting facts about the Eiffel Tower

# data[].attributes.body
Number of lightbulbs = 20 000

Power of each bulb = 6 W

Length of cabling = 40 km

The Eiffel starts twinkling:

1. every day, from 10 pm to 1am

# data[].attributes.body
James Watt invented the steam engine and coined the unit for power as the Watt.

# data[].attributes.body
Inventor of the first carbon filament evacuated light bulb - one year before Edison.

# data[].attributes.attachment_link.title
Ask History: Who Really Invented the Light Bulb? | History

# data[].attributes.body
Energy = the ability to do work.

Power = the rate at which work is done/the rate at which electrical energy is transferred between two points in a circuit.

ENERGY IN A CIRCUIT

A cell forces charge to move in a complete circuit.

The charge is supplied with electrical energy in the cell as a result of chemical reactions that take place inside the cell.

As the charge passes through each component in the circuit, work (W) is done by the cell to drive charge through the component

Electrical energy is converted into other forms of energy in circuit elements.

We say that electrical energy is dissipated in a resistor (converted to other energy forms).

E = W

The work done (W) in moving the electric charge between the ends of a resistor is equal to the energy dissipated in the resistor.

The symbol for electrical energy will also be W.

It is measured in Joules (J) as the unit.

# data[].attributes.headline
HEATERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY 

# data[].attributes.subject
HEATERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY 

# data[].attributes.body
It converts electrical energy into heat energy

# data[].attributes.headline
TOASTERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY

# data[].attributes.subject
TOASTERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY

# data[].attributes.headline
ELECTRICAL ENERGY DISSIPATED IN A CIRCUIT ELEMENT (RESISTOR)

# data[].attributes.subject
ELECTRICAL ENERGY DISSIPATED IN A CIRCUIT ELEMENT (RESISTOR)

# data[].attributes.body
Deriving three equations for electrical energy from fundamental principles:

# data[].attributes.headline
CHECK POINT ON ELECTRICAL ENERGY - DO THIS PROBLEM:

# data[].attributes.subject
CHECK POINT ON ELECTRICAL ENERGY - DO THIS PROBLEM:

# data[].attributes.body
A torch bulb uses two 1,5 V cells connected in series. The bulb has a resistance of 16,3 Ω.

a) Calculate the electrical energy dissipated in the torch bulb in 5 minutes.

b) Calculate the current in the torch bulb.

c) Suppose the same bulb is connected to another battery (for the same length of time) so that the current in the torch bulb is doubled. By what factor would the amount of electrical energy dissipated in the bulb change?

# data[].attributes.headline
POWER DISSIPATED IN A RESISTOR/DELIVERED BY A BATTERY

# data[].attributes.subject
POWER DISSIPATED IN A RESISTOR/DELIVERED BY A BATTERY

# data[].attributes.body
Derive these formulae

# data[].attributes.body
The power value written on any device is the rate at which it can convert electrical energy into other forms of energy.
A value of say 20W means that 20J of energy is converted per second.

# data[].attributes.headline
BRIGHTNESS OF A BULB DEPENDS ON THE POWER DELIVERED TO IT

# data[].attributes.subject
BRIGHTNESS OF A BULB DEPENDS ON THE POWER DELIVERED TO IT

# data[].attributes.body
Explain this:

# data[].attributes.body
An electric kettle is rated at 2,2 kW, 240 V. The supply voltage is reduced from 240V to 230V. Calculate the new power of the kettle.

# data[].attributes.body
Electrical energy consumed is measured in kilowatt hours (kWh).

1 kWh refers to the use of 1 kW of electricity for 1 hour.

1 kWh is equivalent to 3 600 000 J of electrical energy:

1 kWh = 1 000 W × 1 h = 1 000 W × 3 600 s = 3 600 000 J

Electrical consumption is charged per kWh used.

EXAMPLE 1:
Suppose a 1100 W electrical iron is used for 4 hours and the cost of electrical energy is 61c per kWh. What is the cost of using the iron for 4 hours?

Cost = Power rating of appliance (in kW) × time used (in hours) × price per kWh

= 1,1 kW × 4 hours × 61c = 268,4c = R 2,68

EXAMPLE 2:

An electric kettle has a power output of 2,2 kW 240 V.

a) Calculate the current in the kettle.

b) Calculate the resistance of the kettle element.

c) Calculate the cost of using the kettle for 5 hours if the cost per kWh is 61c.

# data[].attributes.attachment_link.title
EMF and internal resistance explained: from fizzics.org

# data[].attributes.body
A cell of unknown emf and internal resistance is connected in series with a 16 Ω resistor and a voltmeter connected across the resistor reads 1,2 V. When the 16 Ω resistor is replaced with an 8Ω resistor, the voltmeter reads 1 V.

a) Draw a neat circuit diagram and explain why the voltmeter reading decreased when the resistance was decreased.

b) Calculate the emf and internal resistance of the cell.

# data[].attributes.body
Watch this video.

# data[].attributes.attachment_link.title
EMF & Internal Resistance - A-level Physics

# data[].attributes.attachment_link.title
A-level Physics Core Practical: EMF and internal resistance

# data[].attributes.headline
To determine the internal resistance of a battery of cells:

# data[].attributes.subject
To determine the internal resistance of a battery of cells:

# data[].attributes.body
Rearrange the equation into the form of a straight line graph  to match the quantities plotted on the graph.

# data[].attributes.body
Emf   =  V ext  +  Ir
V ext  =  -rI      +  Emf
(y  =   mx    +    c)

Where:   y-int  =  Emf
m  =  - r
x   =  I

# data[].attributes.headline
What is the maximum current which can be delivered by the battery?

# data[].attributes.subject
What is the maximum current which can be delivered by the battery?

# data[].attributes.body
For max current (off the graph), Vext = 0.

Hence:

V ext  =  -rI      +  Emf
0  =  -rI      +  Emf
Emf  =  rI
I  =  Emf / r
=  y-int / gradient

# data[].attributes.headline
WITH INTERNAL RESISTANCE IN THE BATTERY:

# data[].attributes.subject
WITH INTERNAL RESISTANCE IN THE BATTERY:

# data[].attributes.body
If more resistors are added in series:

1. The total resistance (𝑅T ) increases.
2. The current in the main circuit will decrease, since the emf of the battery remains constant. (I ∝ 1/R)
3. V lost  will decrease, since the internal resistance remains constant. (V lost = Ir)
4. V ex t  will increase, since the emf remains constant. (by Emf = V ext + V lost)

If more resistors are added in parallel:

1. Total resistance decreases.

2. Current in mains and through the battery increases.

3. V lost increases. (V lost = Ir)

4. Vext will decrease since emf stays constant. (by Emf = V ext + V lost)

Graphs:

In the graph of V ext (measured across battery) vs 𝐼 (measured in a series part of the external main circuit), the emf of the battery is given by the y-intercept (when the load current is 0 A).

# data[].attributes.attachment_link.title
A Level Physics - Internal Resistance and How to Measure it

# data[].attributes.body
p71-75